The present invention relates to a novel ultraviolet-curable oganopolysiloxane composition or, more particularly, to an organopolysiloxane composition curable by irradiation of ultraviolet light at a remarkably high curing velocity with high sensitivity to ultraviolet irradiation.
Ultraviolet-curable organopolysiloxane compositions are known and those comprising a first organopolysiloxane having vinyl groups bonded to the silicone atoms and a second organopolysiloxane having mercapto-substituted hydrocarbon groups bonded to the silicon atoms are disclosed, for example, in Japanese Patent Publications Nos. 54-6512 and 57-34318. The compositions of this type are not quite satisfactory due to the poor storage stability and the surface tackiness of the cured article thereof as well as limited mechanical strengths as a rubbery elastomer so that the rubbery film formed thereof by ultraviolet irradiation is practically disadvantageous. An improved ultraviolet-curable organopolysiloxane composition is disclosed in Japanese Patent Kokai 55-125123 which is a vinyl-containing organopolysiloxane admixed with an organic peroxide. By virtue of the curing accelerating effect of the organic peroxide, such a composition is somewhat advantageous when the rubber article to be cured has a relatively large thickness as a result of the accelerated curing even in the depth of the thick layer. The disadvantages in the compositions of this type are the relatively low curing velocity and the requirement for the wave length of the ultraviolet light which should be in the range from 100 to 300 nm in order to be effective for the curing of the composition. Needless to say, the availability of an ultraviolet light source emitting in such a wave length region is relatively low in comparison with the ultraviolet lamps emitting in the region from 300 nm to visible so that the practical applicability of such a composition is greatly limited.